Over half of the world's population is expected to be overweight or obese by 2035, and the economic impact of rising obesity rates could reach over $4 trillion annually if current trends continue, according to the World Obesity Foundation's (WOF) fifth annual atlas on the global state of obesity.

Obesity rates are rising quickly

In the report, researchers used body mass index (BMI) to assess overweight and obesity. In line with the World Health Organization's guidelines, a BMI over 25 was considered overweight, and a BMI over 30 was considered obese.

According to the report, 51% of the world's population — or roughly 4 billion people — are expected to be overweight or obese by 2035, a significant jump from the 38% of the population who were overweight or obese in 2020.

In addition, the report predicted that the percentage of the global population with obesity will increase from 14% in 2020 to 24% in 2035. Obesity rates are also expected to grow significantly among children and adolescents. Among boys, obesity rates are expected to grow from 10% to 20% between 2020 and 2035, and obesity rate among girls are expected to grow from 8% to 18% during that same period.

In the United States, the annual increase in adult obesity is high at 2.1%, and the percentage of U.S. adults with obesity is predicted to reach 58% by 2035. Among children, the annual increase in obesity is estimated to be 2.4%, and the percentage of U.S. boys and girls with obesity is predicted to be over 40% and close to 35%, respectively, by 2035.

According to Louise Baur, a professor and pediatrician at the University of Sydney and president of WOF, no country has seen their obesity rates, including childhood obesity rates, decline since 1975.

"This means more adolescents now enter adulthood with established risk factors for chronic disease — they're more likely to develop type 2 diabetes, or have heart disease risk factors or orthopedic problems, sleep apnea or fatty liver disease," Baur said.

The cost of growing obesity rates

In the report, researchers assessed both the direct and indirect costs of obesity, including the healthcare costs of 28 obesity-related illnesses, lost economic productivity, and premature death.

Overall, the report estimated that the economic impact of obesity could reach $4.32 trillion annually by 2035 if current trends continue, an increase from $1.96 trillion in 2020. This is equivalent to around 3% of global GDP — or as much as a year of economic growth — and the same impact that COVID-19 had in 2020.

In the United States, the total annual cost of obesity on the country's annual GDP is expected to reach 4% by 2035, up from 3.5% in 2020. However, a separate study from the Milken Institute suggested that that the cost may already be much greater, having reached 9.3% of the annual GDP, or $1.72 trillion, in 2016.

In general, low- and middle-income countries where obesity rates are growing the fastest are expected to bear the highest economic costs.

"The costs are mind-boggling and a really good reason to make the case that any resources allocated to a comprehensive obesity strategy are investments and not costs," said Johanna Ralston, CEO of WFO. "In fact, there's going to be enormous cost savings over time as well as improving people's lives by avoiding complications and premature mortality associated with obesity itself."

According to outside experts, even though the report's cost projections are high, they are likely an underestimate since they do not account for several factors that could impact obesity-related costs.

For example, Barry Popkin, a professor of nutrition at the UNC Gillings School of Global Public Health at the University of North Carolina, noted that the report ignores "the entire issue of long-term disability in their calculations."

The report also did not account for potential costs and savings associated with new weight loss drugs, such as Ozempic or Wegovy. Although these drugs are expensive, they may also reduce the long-term costs and risks of obesity and any associated conditions, including Type 2 diabetes.

In addition, the report did not consider the potential economic impact of weight stigma, which can affect how much people, especially women, earn. According to an Economist analysis, overweight women tend to have lower salaries, and women with obesity may earn 10% less.

"That is a tremendous cost that is probably not reflected in any of the direct medical costs," said William Dietz, director of the Sumner M. Redstone Global Center for Prevention and Wellness at George Washington University. "And it may contribute to medical costs, because among the most biased and stigmatizing people in the life of a person with obesity are physicians."

As obesity rates rise and the economic impact increases, health experts have encouraged governments to enact policies that address the issue before it's too late. (Belluz, STAT, 3/2; Sforza, The Hill, 3/2; Moniuszko, CBS News, 3/3; Reuters, 3/2; Lobstein et al., World Obesity Federation, accessed 3/3)